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  <title>Document</title>
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  <script>
    // 数组喝字符串内置对象不能给原型对象覆盖操作Array.prototype = {}
    // 只能是Array.prototype.xxx = function(){}的方式
    
    //原型对象的应用 扩展内置对象方法   
    Array.prototype.sum = function(){
      var sum = 0;
      for(var i =0;i < this.length;i++){
        sum += this[i];
      }
      return sum;
    }
    // Array.prototype = {
    //   sum: function() {
    //     var sum = 0;
    //     for(var i = 0; i < this.length; i++){
    //       sum += this[i];
    //     }
    //     return sum;
    //   }
    // }
    var arr = [1,2,3];
    console.log(arr.sum());
    console.log(Array.prototype);
    var arr1 = new Array(11,22,33);
    console.log(arr1.sum());
  </script>
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